Open clinical trials of isotretinoin in schizophrenic patients on and off of haloperidol have suggested a possibly beneficial synergism between haloperidol and isotretinoin in the treatment of psychotic illness. This has been supported by the results of animal studies of the direct and synergistic (with haloperidol) effects of isotretinoin on animal behavior. Therefore, this project has been initiated to evaluate these potential effects in a placebo controlled, double blind, cross over study. Also, other possible effects including changes in visual and auditory sensory processes will be monitored electrophysiologically.